Treatment of subsurface earth formations



" tates The present invention is directed to a method for treating a subsurface earth formation. More particularly, the invention is concerned with increasing production of oil by fracturing a subsurface earth formation. In its more specific aspects, the invention is concerned with a method for treating a subsurface earth formation in which sand is deposited in and adjacent to a subsurface earth formation.

The present invention may be briefly described as a method for fracturing a subsurface earth formation with water containing a sand-propping agent in which the sand-propping agent is lodged in the resulting fractures to maintain them open. A particular feature of the present invention is rendering the sand-propping agent oil wet whereby the tendency of the sand-propping agent to settle out of the water is decreased or substantially depressed.

The present invention also involves treating a subsurface earth formation with a suspension of sand in the water in which the sand has been wet with oil, the suspension being introduced into the subsurface earth formation through a well bore penetrating the subsurface earth formation to deposit the hydrocarbon-wet sand in and adjacent to the subsurface earth formation.

In the hydraulic fracturing of subsurface earth formations, the use of aqueous hydraulic fracturing fluids has been limited heretofore because of the inability of the fluid to carry sand adequately at low pump rates. Typical aqueous fracturing fluids may have sand falling rates of 20 feet per minute or more. If the pumps introducing the aqueous fracturing fluid into a Well are stopped during a fracture treatment, the sand will usually deposit in the well and form a bridge. In accordance with the present invention, the tendency of the sand to pack tightly and to deposit and clog a well bore is decreased or entirely suppressed. The present invention involves preferentially wetting the sand with an oil wetting surface-{active agent contained in a hydrocarbon phase. Water is added to the oil-wet sand in such quantities that any latent water-in-oil emulsion is broken by an excess of Water phase. The effect is to make the individual sand grains less adherent with respect to each other and with respect to the tubing or pipe string through which the sand grains are introduced. A particular advantage of wetting the sand with hydrocarbon when used in a water suspension is that higher concentrations of" sand may be employed than are normally used in fracturing or treating operations in that the sand assumes a fluidized condition in the suspension in the water.

in accordance with the present invention, certain surface-active agents are employed which cause preferential wetting of the sand with the liquid hydrocarbon. These surface-active agents are those which have a hydrophilelipophile balance in the range between about to about 8. Hydrophile-lipophile balance (HLB) is a term recognized in the art and is described by W. C. Griflin in The Journal Society Cosmetic Chemists, vol. 5, page 249 (1954), and also Emulsions: Theory and Practice, Reinhold Publishing Corp, New York, 1957, at pages 189 to 196.

The surface-active agents employed in the practice of the present invention for preferentially wetting the sand with hydrocarbon may be illustrated by compounds such as sorbitan monooleate, sold under the trade name of Span sorbitan sesquioleate, sold under the trade name of Arlacel C; sorbitan trioleate, known to the trade as Span diglycol laurate; diglycol oleate; and other compounds which have this property. As illustrations of other com-pounds useful in this invention, mention is made of: polyoxyethylene sorbitol beeswax derivative, sorbitan tristearate, polyoxyethylene sorbitol hexastearate, ethylene glycol fatty acid ester, propylene glycol fatty acid ester, propylene glycol monostearate, polyoxyethylene sorbitol 4.5 oleate, glycerol monostearate, propylene glycol monolaurate, diethylene glycol monooleate, diethylene glycl fatty acid ester, diethylene glycol monostearate, glycerol monostearate (self-emulsifying), diethylene glycol monolaurate (soap free), sorbitan monopalmitate, polyoxyethylene dioleate, tetraethyleneglycol monostearate, polyoxypropylene ma-nnitol dioleate, polyoxyethylene sorbitol lanolin oleate derivative, and polyoxypr-opylene stearate.

The amount of the surface-active agent or salt having a low HLB value may range from about 0.2 to about 5 percent by weight based on the water. A preferred amount may range from about 0.5% to about 2% by weight.

The liquid hydrocarbon employed in the practice of the present invention to wet the sand is suitably one having a viscosity from about 1.5 to about 400 centipoi-ses at 60 F. and boiling in the range from about to about 800 F. Illustrative of the liquid hydrocarbons may be mentioned the gasoline, kerosene, diesel oil, and gas oil hydrocarbons and the individual components thereof. Kerosene, diesel oil, and crude oils are preferentially used. While liquid hydrocarbon fractions obtained from crude petroleum and the like may be satisfactory, under some instances it may be desirable to employ pure hydrocarbons boiling Within the range of about 100 to about 800 F.

In practicing the present invention, the sand employed is usually round Ottawa sand having a mesh size (U.S. Sieve Series) in the range from about 10 to about 40 mesh. Equivalent sand to the round Ottawa may be used and different mesh sizes may be employed. For example, angular sand grains may be used and either angular or round sand having mesh sizes from about 10 to about 80 may be used. The sand may be between 20 to 40 mesh, 40 to 60 mesh, or 60 to 80 mesh, or may be distributed over the range of mesh sizes. When employing the present invention in fracturing subsurface earth formations, 20 to 40 mesh Will be preferred while when the present invention is employed in forming a deposit or pack in the well, 10 to 40 mesh may be used.

The amount of sand employed in the practice of the present invention may range from about .1 pound per gallon of the Water used as a suspending medium and as a fracturing liquid to about 5 pounds per gallon of water. A preferred range is from about 0.5 to about 3 pounds per gallon of water. As an example, about 10,000 to 15,000 pounds of sand may be used for each 10,000 gallons of the water used as a suspending medium.

The water employed as a suspending medium and/or as a fracturing liquid may be either fresh water or a brine. In fact, it is preferred to employ a brine such as sodium chloride or calcium chloride which contains from about 1 to about 5 percent of either the sodium chloride or the calcium chloride. From about 2 to about 3 percent by weight of either the sodium chloride or the calcium chloride may be used.

In practicing the present invention, a solution of a low HLB oil-soluble surface-active agent may be made up into a hydrocarbon such as kerosene and then admixed thoroughly with sand. The resulting hydrocarbon-Wet sand then has water added to it in sufiicient amounts to form a suspension, and the suspension is then pumped into or introduced into a well bore piercing a subsurface earth formation. When the suspension is used to fracture a subsurface earth formation, the suspension may be introduced through a pipe string under sufficient pressure to cause the fracture or opening up of fissures in the subsurface earth formation with the resulting lodgement of the oil-wet sand in the so-formed fractures or fissures. Thereafter hydrocarbons may be produced from the fractured formation into the well bore and conducted to the earths surface through the usual pipe or tubing string.

The present invention also contemplates the formation of a deposit or pack around a casing lining the wall of the well in a subsurface earth formation from which fine sand is produced in suificient quantity to interfere with the production of desirable hydrocarbons. When such is the case, in the practice of the present invention a suspension of hydrocarbon or oil-wet sand in water is introduced into the usual cavity back of the casing and the sand formed into a pack such that it retains the fine sand which would ordinarily be produced with the hydrocarbons from the formation. It is also contemplated in this aspect of the present invention that a deposit or pack may be formed around a screen and liner by introducing into the screen and liner and out through the perforations therein a suspension of hydrocarbon or oil-wet sand in water to deposit the hydrocarbon or oil-Wet sand back of the screen and liner to retain the fine sand which ordinarily would be produced with the hydrocarbons from the formation.

The present invention is particularly applicable to treatment of subsurface earth formations or Zones which contain natural gas hydrocarbons. It is therefore contemplated that the present invention may have specific application to fracturing sands or rock which contain substantial quantities of gas. However, it is to be understood that the invention is not to be limited to fracturing formations which contain natural gas hydrocarbons and the like but is also adapted to fracturing formations which contain liquid hydrocarbons. However, when the invention is used in fracturing formations containing liquid hydrocarbons or in treating such formations, it maybe desirable to treat the sand which is lodged in the fractures or formed into a pack and which has been wet with oil with a surface-active agent having a high HLB value in the range from about 13 to about 40. Such surface-active agents which may be employed to make the oil wet-sand preferentially water-wet may he exemplified by a compound such as polyoxyethylene stearate, which is sold to the trade as Myrj 52; Arquad 12, a quaternary ammonium alkyl compound; Tween 20, a polyoxyethylene sorbitan monolaurate; Brij 35, which is a polyoxyethylene stearate; Glim, which is the trade name for ethylene-oxide condensation product of an alkyl phenol; Alrose O, which is fatty alkylol amide condensation product; Alkaterge C, a substituted oxazoline; Alkanol WXM, which is a sodium salt of monoamyl naphthalene. Other compounds which have HLB values in the range from about 13 to about 40 may also be used.

As a specific example, oil-Wet sand may be suspended in an aqueous fracturing fluid as follows: 2 /2 gallons of low HLB oil-soluble surface-active agent such as Span 80, Aptet 277, which is tall oi-1 reacted with ethyleneoxide, or oleic acid, or other low HLB surface-active agent, are added to 50 gallons of kerosene and the mixture then added to 5,000 pounds of sand and intimately contacted therewith. Water containing sodium chloride or calcium chloride in a desired concentration in a sufficient .amount is then added to fluidize the oil-wet sand. The hydrocarbon-wet sand is then pumped into a well and the suspension is then forced into a formation under sufficient pressure to cause fracturing thereof.

The present invention is quite advantageous and useful in that the hydrocarbon-wet sand is pumpable and does not form packs or bridges across a pipe string which resists removal from the well. In short, wetting of the sand with oil when it is suspended in water renders the sand in a fluidized condition which may increase the ease of fracturing. In other words, in the practice of the present invention there are numerous advantages such that the sand is maintained suspended in the water for a sufficient length of time that it may be readily pumped or introduced into contact with or adjacent a subsurface earth formation. As stated hereinbefore, the oil-wet sand does not pack tightly and deposit readily from the aqueous fluid at low pump rates. Also, the hindered settling rate in accordance with the present invention allows the use of aqueous fluids with a high sand concentration Without sanding up the well which heretofore would require the use of drilling operations and the like.

The nature and objects of the present invention having been completely described and illustrated, what we wish to claim as new and useful and secure by Letters Patent 1. In a method for fracturing a subsurface earth formation with 'a suspension of water containing a sand-propping agent in which the sand propping agent is lodged in and m'aitains the resulting fracture open, the improvement which comprises rendering the sand-propping agent wet with hydrocarbon by contacting the sand-propping agent with a composition consisting essentially of a liquid hydrocarbon and "a surface-active agent having a low HLB in the range from about 0 to about 8 prior to suspending it in said water whereby the tendency of the sand-propping agent to settle is decreased.

2. A method for fracturing a subsurface earth formation which comprises forming a composition consisting essentially of a liquid hydrocarbon and a surface-active agent having a low HLB in the range from about 0 to about 8, contacting sand with said solution to cause said sand to be wet with said hydrocarbon, forming a suspension of said hydrocarbon-wet sand in water, and then fracturing a subsurface earth formation with said suspension whereby said oil-wet sand is lodged in the resulting fractures.

3. A method in accordance with claim 2 in which the hydrocarbon is kerosene.

4. A method in accordance with claim 2 in which the hydrocarbon is diesel oil.

5. A method in accordance with claim 2 in which the hydrocarbon is crude oil.

6. A method in accordance with claim 2 in which the hydrocarbon is a fraction of crude oil.

7. A method for fracturing a subsurface earth formation which comprises admixing sand with a composition consisting essentially of a liquid hydrocarbon and a sufiicient amount of a surface-active agent having a low HLB in the range from about 0 to about 8 to cause said sand to be wet with said hydrocarbon, forming a suspension of said hydrocarbon-wet sand in water, and then pumping said suspension into a well bore piercing said subsurface earth formation under suflicient pressure to form fractures in said subsurface earth formation and to lodge said hydrocarbon-wet sand in :said fractures.

8. A method in accordance with claim 7 in which the subsurface earth formation contains gaseous hydrocarbons.

9. A method in accordance with claim 7 in which the subsurface earth formation contains liquid hydrocarbons.

10. A method in accordance with claim 7 in which the water contains sodium chloride.

11. A method in accordance with claim 7 in which the water contains calcium chloride.

12. A method in accordance with claim 7 in which the oil-wet sand is treated with a surface-active agent having a high HLB in the range irom about 13 to about 40 after sand is placed in the fractures.

13. A method in accordance with claim 7 in which the amount of the surface-active agent having a low HLB is within the range =from about 0.2% to about 5.0% by weight, based on the water in which the hydrocarbon-Wet sand is suspended.

14. A method for treating a subsurface earth formation which comprises forming a composition consisting essentially of a liquid hydrocarbon and a surface-active agent having a low HLB in the range from about to about 8, contacting sand with said solution to cause said sand to be wet with said hydrocarbon, forming a suspension of said hydrocarbon-wet sand in water, and then introducing said suspension into a well bore penetrating said subsurface earth formation whereby said hydrocarbon-Wet sand is deposited in said subsurface earth formation.

15. A method in accordance with claim 14 in which the 20 6 hydrocarbon has a viscosity from about 1.5 to about 400 centip oises at F. and boils in the range from about to about 800 F.

16. A method for fracturing a subsurface earth formation which comprises forming a composition consisting essentially of an oil and a surface-active agent having a low HLB in the range from about 0 to about 7, contacting sand with said solution to cause said sand to be wet with said oil, forming a suspension of said oil-wet sand in water, and then fracturing a subsurface earth formation with said suspension whereby said oil-wet sand is lodged in the resulting fracture.

References Cited in the file of this patent UNITED STATES PATENTS 2,742,426 Brainerd Apr. 17, 1956 2,802,531 Cardwcll Aug. 13, 1957 2,960,465 Ten Brink NOV. 15, 1960 

1. IN A METHOD FOR FRACTURING A SURFACE EARTH FORMATION WITH A SUSPENSION OF WATER CONTAINING A SAND-PROPPING AGENT IN WHICH THE SAND PROPPING AGENT IS LODGED IN AND MAINTANS THE RESULTING FRACTURE OPEN, THE IMPROVEMENT WHICH COMPRISES RENDERING THE SAND-PROPPING AGENT WET WITH HYDROCARBON BY CONTACTING THE SAND-PROPPING AGENT WITH A COMPOSITION CONSISTING ESSENTIALLY OF A LIQUID HYDROCARBON AND A SURFACE-ACTIVE AGENT HAVING A LOW HLB IN THE RANGE FRON ABOUT 0 TO ABOUT 8 PRIOR TO SUSPENDING IT IN SAID WATER WHEREBY THE TENDENCY OF THE SAND-PROPPING AGENT TO SETTLE IS DECREASED. 